Among spontaneous speeches, there are speeches having a faster-than-normal utterance rate or a slower-than-normal utterance rate. As one of the methods for recognizing such speeches, a method is known in which an utterance rate classifier and a plurality of utterance-rate-dependent models are used.
However, in the conventional technology, there occurs an increase in the processing load because of performing an operation of determining the utterance rate. Moreover, since a plurality of models is used, it becomes necessary to have a larger memory area.